NAME

       mutt_dotlock - Lock mail spool files.

SYNOPSIS

       mutt_dotlock [-t|-f|-u|-d] [-p] [-r retries] file

DESCRIPTION

       mutt_dotlock  implements  the  traditional  mail  spool  file  locking method: To lock file, a file named
       file.lock is created. The program operates with group mail privileges if necessary.

OPTIONS

       -t     Just try.  mutt_dotlock won't actually lock a file, but inform the invoking process if it's at all
              possible to lock file.

       -f     Force the lock.  If another process holds a lock on file longer than a  certain  amount  of  time,
              mutt_dotlock will break that lock by removing the lockfile.

       -u     Unlock.  mutt_dotlock will remove file.lock.

       -d     Delete.   mutt_dotlock  will  lock  file,  remove  it  if  it  has length 0, and afterwards remove
              file.lock.

       -p     Use privileges.  If given this option, mutt_dotlock will operate with group mail  privileges  when
              creating and deleting lock files.

       -r retries
              This  command  line option tells mutt_dotlock to try locking retries times before giving up or (if
              invoked with the -f command line option) break a lock.  The  default  value  is  5.   mutt_dotlock
              waits one second between successive locking attempts.

FILES

       file.lock
              The lock file mutt_dotlock generates.

SEE ALSO

       fcntl(2), flock(2), lockfile(1), mutt(1)

DIAGNOSTICS

       mutt_dotlock gives all diagnostics in its return values:

       0 - DL_EX_OK
              The program was successful.

       1 - DL_EX_ERROR
              An  unspecified  error such as bad command line parameters, lack of system memory and the like has
              occurred.

       3 - DL_EX_EXIST
              The user wants to lock a file which has been locked by another process already.   If  mutt_dotlock
              is  invoked  with  the  -f  command line option, mutt_dotlock won't generate this error, but break
              other processes' locks.

       4 - DL_EX_NEED_RPIVS
              This return value only occurs if mutt_dotlock has been invoked with the -t  command  line  option.
              It means that mutt_dotlock will have to use its group mail privileges to lock file.

       5 - DL_EX_IMPOSSIBLE
              This  return  value  only occurs if mutt_dotlock has been invoked with the -t command line option.
              It means that mutt_dotlock is unable to lock file even with group mail privileges.

NOTES

       mutt_dotlock tries to implement an NFS-safe dotlocking method which was borrowed from lockfile (1).

       If the user can't open file for  reading  with  his  normal  privileges,  mutt_dotlock  will  return  the
       DL_EX_ERROR  exit  value  to  avoid  certain attacks against other users' spool files. The code carefully
       avoids race conditions when checking permissions; for details of all this see the comments in dotlock.c.

HISTORY

       mutt_dotlock is part of the Mutt mail user agent package.  It has been created to avoid running mutt with
       group mail privileges.

AUTHOR

       Thomas Roessler <roessler@does-not-exist.org>

Unix                                               AUGUST 1999                                        dotlock(1)